1. Field of the Invention
This invention relates to a method and system for fusing information from multiple images and, in particular, relates to a method for fusing information from multiple images in a mammographic computer-aided detection (CAD) system.
2. Discussion of Background
Breast cancer is the second most common cancer among women, after non-melanoma skin cancers. Currently, slightly more than two million women living in the United States have been diagnosed with and treated for breast cancer. More than 1.2 million people will be diagnosed with breast cancer this year worldwide according to the World Health Organization. In the United States alone, the American Cancer Society estimates that in 2004, approximately 215,990 women will be diagnosed with invasive breast cancer (Stages I-IV) and another 59,390 women will be diagnosed with in situ breast cancer, a very early form of the disease. Further, an estimated 1450 cases of breast cancer will be diagnosed in men in 2004.
Additionally, breast cancer is the second leading cause of cancer death in women, exceeded only by lung cancer. In 2004, about 40,110 women and 470 men will die from breast cancer in the United States. However, the good news is the death rates from breast cancer have declined significantly between 1992 and 1996, with the largest decreases coming from younger women under the age of fifty. Medical experts attribute the decline in breast cancer deaths to better detection and more effective treatments at an earlier stage. The early detection of breast cancer helps reduce the need for therapeutic treatment and minimizes pain and suffering, which allows women to continue to lead happy and productive lives.
Mammography has improved detection rates—and therefore survival rates—over the past several decades. More women than ever are being screened by mammography. In 1987, twenty-nine percent of American women surveyed said they received a mammogram every two years, versus seventy percent in 2000. Further, in 2000, sixty-three percent of American women said they were going for a mammogram every year. This increased usage has translated into more early cancers being diagnosed, which in turn has translated into better survival odds. According to the American Cancer Society, when breast cancer is confined to the breast, the survival rate is close to 100%. A woman with invasive carcinoma today is thirty-nine percent less likely to die from her disease than she would have been back in the 1980s. Most of the decrease can be attributable to screening mammography.
Screening mammography is used to look for breast disease in women who are asymptomatic, that is, they appear to have no breast problems. Screening mammography commonly provides two views (x-ray pictures) of each breast, cranio-caudal (CC) and medial-lateral oblique (MLO). In a CC view, the breast is compressed between paddles that are oriented parallel to the axial plane. In a MLO view, the compression paddles are oriented in a plane obtained by rotating the sagittal plane towards the axial plane by approximately 30 degrees. These standard views are used in the vast majority of screening exams in the United States.
Over the past two decades, CAD systems have been developed to help radiologists detect suspicious abnormalities on mammograms. This is accomplished most commonly with screen-film mammography and less often with digital mammography. Early research results suggest that CAD systems help radiologists diagnose more early stage cancers than mammography alone, especially in some of the threshold cases. The CAD system, in essence, functions as a second reader of the mammographic images. The CAD system marks regions on the image that indicate areas of interest such as, for example converging lines and shadows indicating a possible spiculated mass, densities with irregular margins that may indicate the onset of cancer and clusters of bright spots that may be malignant cancer. Therefore, one of the objectives of a mammographic CAD system is to indicate to the radiologist the tissue regions that need medical attention while leaving normal tissue unmarked.
One way to improve CAD performance is to exploit information from the multiple images obtained from a typical mammography examination. Additionally, information can be obtained by incorporating images from a prior mammographic examination with information with the current examination.
Therefore, a need exists for a method to improve performance of CAD systems by fusing image information from all images of the current examination as well as from images of previous mammographic examinations.